Oh Louise, huge huge (gentle) hugs for you 
OCD is a bastard, I know it too well.
You recognise that your problem is one of worry - you have said as much. You know that no alcohol was ingested and that even if you drank it would not harm the baby. You don't believe your baby has been harmed. So really you are recognising that the content of this ever shifting obsessions is irrelevant.
Now, if the problem was actually one of germs, it would be right to take precautions to avoid germs. But if the problem is one of excessive worry about germs then those precautions would make the problem worse - setting ever higher unnecessary standards you can't meet and making you ever more hyper-vigilant. The same for bumps. The same for avoiding alcohol.
You know for every precaution or ritual we attach importance to, we're set up for more distress when we can't reach unrealistic standards.
Actually kissing your DP on the lips when he has drunk beer would have made a good deliberate exposure. It was not a mistake at all - I am afraid that is example of well meaning relatives not having a clue what to say or do. They give every response they can think of to try and help, including nonsensical unhelpful ones.
All this time you have avoided alcohol has reinforced the idea that it is dangerous, your brain thinks it must have risky because you made such an effort to avoid it. If you went and took a sip of beer now, and again tomorrow, and the next day...eventually your brain would go the opposite way and think 'oh, this can't be dangerous because we're doing it willingly'. Unfortunately the fear part of our brain doesn't seem to be able to filter out the illogical by thinking, it takes action. I can't do it yet! But I will keep trying.
Keep telling the medical staff everything - they won't take your baby away. You need to tell them so that every bit of support you can access is put in place. I think medication will help with this but it may take a while to kick in. I think you would be fine to take it at this stage, but I understand that might not take it till the birth. You're so nearly there. It will all be ok, I promise you it will.
Your DH should really read some books on OCD and know the enemy as soon as possible.
I know none of what I have said will help. I have this disease too. But we have to keep trying. I just want you to know that I understand and am sending you lots of virtual love. If there is anything I can do or say to help, let me know.